الفهرس 
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Abstract
The present thesis introduces a study and investigation for
numerical simulation of the performance of a muffler (silencer) of
internal combustion engine. Muffler (silencers) are widely used in both
internal combustion engines and blowers to minimize exhaust noise.
In the current work, a three-dimensional (3-D) time-domain
computational fluid dynamics (CFD) model is developed for
modelling for the airflow in the muffler. The plane wave
decomposition method are used to forecast the transmission loss of
reactive silencers. The incompressible flow form of Navier–Stokes
equations with the realizable k–ε turbulent flow model using enhanced
wall treatment of turbulence are solved for this purpose using finite
volume solver ANSYS FLUENT-19.2 commercial package. The
objective of this dissertation is to enhance the transmission loss for
better damping for sound pressure wave
The ensuing unstable flow calculations are started with a steady
flow computation that is completed using a mass-flow-inlet boundary
condition. To execute the initial computation of unstable flow, an
impulse (acoustic excitation) is applied over the constant mass flow at
the model’s intake. Upon complete propagation of the impulse wave
into the silencer, the non-reflecting boundary condition (NRBC) is
included. A second unsteady flow computation is carried out for the
case where there is no acoustic stimulation at the intake. The time
histories of both pressure and velocity at the upstream and downstream
are examined at certain locations, as well as the pressure history at the
downstream measuring point, are recorded during the two transient
calculations. There are differences between the two unstable flows in the associated auditory values. Consequently, the incident sound
pressure signal is derived by using plane wave decomposition
upstream and the transmitted sound pressure signal is only the sound
pressure downstream. Following the Fast Fourier Transform (FFT) to
transfer the two sound pressure signals from the time domain to the
frequency domain, the transmission loss (TL) of the silencer is
computed. In order to enhance the transmission loss TL of airflow
inside the muffler, three different schemes are adopted and
investigated. The first scheme deals with the effect of increasing the
number of perforated holes in the transverse section. While the second
studies the effect of increasing the number of perforated holes in the
longitudinal section. The last one investigates the effect of muffler
chamber profile from circular profile to elliptic profile with different
aspect ratio followed by the investigation of perforated pipe orientation
in this elliptic profile.
In addition to improving the geometry by adding more holes to
the muffler’s cross-section, the numerical calculations and the provided
data correspond well with the published results. The best optimum
geometric shape for the muffler chamber is analysed by changing the
circular shape to an elliptic one with a different ratio. The numerical
calculations and the reported data showed that the TL increases with
the increase of number of holes in the cross section area and with
changing chamber profile to ecliptic shape at aspect ratio of 1.2.